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New Scientist Live

Antique fridge could keep Venus rover cool

By David Shiga

A rover that could survive the intense heat of Venus, seen here in an artist’s impression, could revolutionise our understanding of the planet (Illustration: NASA)

Electronics for the rover are contained at the front of the vehicle in a green sphere, which is only partly visible through gaps in the vehicle frame. Green cylinders represent cameras, and the red object at the front is a robotic arm that has science instruments mounted on it (Illustration: Shawn Krizan/NASA)

A high-tech refrigeration system could keep a rover functioning for weeks on the searingly hot surface of Venus, say NASA researchers. A long-lived Venus rover could help scientists understand why Venus, with its runaway greenhouse effect, has become so different from Earth.

The surface of Venus broils at a temperature of about 450 °C – hot enough to melt lead. Several probes in the Soviet Venera and Vega series, as well as a NASA Pioneer Venus probe, landed on Venus and returned data from the surface in the 1970s and early 1980s. But they all expired in less than 2 hours because of the tremendous heat.

Now, two NASA researchers have designed a refrigeration system that might be able to keep a robotic rover going for as long as 50 Earth days. The work was carried out by Geoffrey Landis and Kenneth Mellott of NASA’s Glenn Research Center in Cleveland, Ohio, US.

The main concern is keeping the electronics cool. The NASA pair plan to do this by packing the electronics in a ceramic-based insulator and placing it inside a metal sphere about the size of a grapefruit.

Stirling cooler

Heat would then be pumped out of the sphere using a Stirling cooler, which works by compressing and then expanding a gas with a piston. When the gas expands, it cools down, absorbing heat from the electronics chamber. Then, as the gas is compressed and its temperature rises, the heat is allowed to dissipate in the atmosphere via a radiator.

Stirling coolers were invented in 1816 by Reverend Robert Stirling, a Scottish clergyman, but were largely ignored until the mid 20th century, when their impressive energy efficiency became better known.

They are already used on Earth to cool equipment in deep shafts drilled in rock for oil exploration, and are being developed for use in energy-saving home refrigerators. Landis and Mellott have now designed one suitable for use in the incredibly hot environment of Venus.

But to dissipate heat, the radiator has to be hotter than the surrounding atmosphere, so the new design can reach 500 °C. The cool end of the Stirling engine would keep the rover’s innards at a relatively chilly 200 °C, which should allow commercially available electronics to operate well.

The researchers say the power to run the Stirling cooler, about 240 watts, would be provided by on-board plutonium batteries, which generate power from the heat of radioactive decay.

“The next step is probably going to be trying to build some prototypes and just demonstrate that what we are proposing is something that’s going to work,” Landis told New Scientist.

Challenging mission

NASA has not committed to a Venus rover mission, but Landis notes that a 2003 National Academies of Science study recommended that high priority be given to a robot mission to investigate the Venusian surface. Landis thinks a Venus rover could become a reality within a decade or so.

But such a mission is not without its challenges, says Venus researcher Mark Bullock of the Southwest Research Institute in Boulder, Colorado, US. “I think that a long-lived rover on Venus is a very, very difficult mission,” he told New Scientist.

However, he thinks the Stirling cooler is a promising approach&colon; “Active cooling is essential, and the Stirling cycle cooler with a radioisotope power source is probably the very best way to do it.”

Putting a long-lived rover on the surface of Venus could revolutionise our understanding of the planet, helping to answer such questions as why Venus ended up so different from Earth, he says. Many scientists suspect Venus was much cooler in the past, and was perhaps even covered with oceans of liquid water where conditions could have been friendly to life.